One Ross's Gull in Washington would be a very rare bird, but more than one
would be unheard of. Here's some information on them in WA.

http://www.birdweb.org/birdweb/rare_species.asp?id=211

Kevin Li
King County Environmental Lab
322 West Ewing St.
Seattle, WA 98119
(206) 684-2344
http://dnr.metrokc.gov/wlr/locations/envlab.htm